The state of the art in film manufacturing is known as epitaxial growth. Epitaxy (from Greek epi meaning <<on>> and taxis meaning <<ordered arrangement>>) refers to ordered growth of a layer of a given material on the surface of a substrate, whereby the crystal structure and orientation of the growing layer reproduce those of the substrate. The epitaxial growth of single crystal layers of inorganic materials on inorganic substrates is widely used in modern semiconductor technology. There are two basically different processes: (i) gas- or vapor-phase epitaxy (VPE), whereby thin layers are deposited onto substrates from gas or vapor mixtures, and (ii) liquid-phase epitaxy (LPE), whereby the growth proceeds from liquid solutions or melts. In the former process (VPE), atoms of an inorganic material to be deposited are vaporized in vacuum or in a buffer gas atmosphere, transferred by diffusion or convection driven by the temperature gradient from the source occurring at a higher temperature to a colder substrate, and deposited there in the form of a thin layer. Atoms of the inorganic deposit migrate over the substrate surface until occupying a position characterized by a minimum energy at an active surface center. The role of such active centers can perform, in particular, by the various irregularities of the surface structure. In the course of the epitaxial layer growth, new irregularities and, hence, active centers can appear. Alternatively, when supersaturation exceeds the critical level, atoms exhibit condensation into a liquid phase or crystallize in the gas phase in the region of lower temperatures at the substrate. In this case, atomic agglomerates in the form of liquid drops or solid microcrystals are deposited onto the substrate surface. Sufficiently small microcrystals can be oriented on the surface, while large crystals settle with an arbitrary orientation. In the latter case, the system exhibits the growth of unoriented polycrystalline layer. It must be noted that epitaxial growth requires using crystalline substrates with parameters of the crystal unit cell matched with those in the growing thin crystal layer. In this case, the growing crystal structure repeats that of the substrate. The substrate-induced ordering of the epitaxial layer (epilayer) is explained by the tendency of any system to possess a minimum free energy. This trend is manifested in that the nuclei of the epitaxial layer acquire the orientation corresponding to a minimum free energy, which is possible when there is a certain correspondence between the arrangement of atoms in the adjacent crystal planes.
There are known methods for the epitaxial growth of thin layers composed of large anisotropic organic molecules on inorganic substrates. One method of the epitaxial growth of thin organic films (perylenetetracarboxylic dianhydride and perylene) on an inorganic semiconductor surface (e.g., Si (111) wafers) was described by U. Zimmermann, G. Schnitzler et al. [Epitaxial Growth and Characterization of Organic Thin Films on Silicon, Thin Solid Films 174, 85-88 (1989)]. An example when such an organic material (3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA)) evaporated onto Ag (111) substrate formed a highly ordered thin film was demonstrated by L. Chkoda, M. Schneider et al. [Temperature-Dependent Morphology and Structure of Ordered 3,4,9,10-Perylenetetracarboxylic Acid Dianhydride Thin Films on Ag (111), Chem. Phys. Lett. 371, 548-552 (2003)]. The results of investigation of the initial growth stages of the organic molecular semiconductor PTCDA films on In-terminated InAs (001) were reported by C. Kendrick and A. Kahn [Epitaxial Growth and Phase Transition in Multilayers of the Organic Semiconductor PTCDA on InAs (001), J. Crystal Growth 181, 181-192 (1977)].
The method of manufacturing of the ordered copper phthalocyanine (CuPc) films on graphite by molecular beam deposition in vacuum is known [Wataru Mizutani, Youichi Sakakibara et al., “Measurements of Copper Phthalocyanine Ultrathin Films by Scanning Tunneling Microscopy and Spectroscopy”, Japanese Journal of Applied Physics, Vol. 28, No. 8, August, 1989, pp. L 1460-L 1463]. In this method the pressure in the vacuum chamber, prior to and during the deposition, is supported at a level 10−10 Torr and 2×10−8 Torr, respectively. The rate of film growth is maintained at about 0.5 nm/min. The temperature of the substrates is held at 15° C. during the deposition. The orientation of the molecules on graphite is measured by X-ray diffraction. The CuPc molecules are mainly arranged with the molecular planes nearly parallel to the substrate, but there are weak diffraction peaks indicating the existence of the molecules perpendicular to the substrate. Average thicknesses of the CuPc films vary from 0.4 nm (about one layer) to 20 nm. In the films, which thickness is equal to approximately 20 nm, the grain structures are found. In the case of monolayer deposition of phthalocyanine on graphite, the molecules are thermally activated at room temperature and form the islands at stable sites. When more than one layer covers the substrate, the thermally activated motion is suppressed by the interaction between the neighboring molecules, so that the islands are formed on the surface of the films. In the course of formation of the films, the unevenness of the deposition can be caused by dust, defects of the substrate, etc. These nonuniformities can be the nuclei of the islands or the grains. As the film thickness increases, those nonuniformities also grow to give perpendicular arrangement of the molecules on the substrate. Thus, the known method does not allow making the globally oriented and anisotropic films.
There are several disadvantages inherent in inorganic single crystals, which limit the possibilities of using such crystals as substrates for epitaxial growth. In particular, the number of single crystal materials suited for epitaxial growth is rather restricted because the crystal surface can be reactive, and/or covered with oxides, and/or contain adsorbed water molecules. The substrate can be nontransparent, possess undesired electronic and/or thermal properties, and so on. The major restriction is based on the requirement of matched (coinciding or co-dimensional) crystal lattices of substrate and growing crystal layer.
There are many optical application requiring epitaxial layers possessing anisotropic optical properties. This implies that the substrate must possess anisotropic properties as well. This present invention is directed to method and structure which overcome many of the shortcomings of the methods of forming epitaxially grown layers of the prior art as described above.